Axial columns with packed beds of particles are commonly used both in process scale chromatography and in solid-phase synthesis of e.g. peptides or oligonucleotides. In chromatography, the bed contains adsorbent particles for selectively binding and certain feed components and in solid phase synthesis the particles used have suitable reactive groups for stepwise synthesis of the peptide or oligonucleotide. In such columns, the packed particle bed is usually stabilized by compression in an axial direction, sometimes using a movable adaptor (which can alternatively be called a piston). Traditionally the adaptor has been movable by means of threaded rods or hydraulics, but more recently columns with adaptor movement controlled by step motors have also become available.
The particle bed is confined between two bed supports, which typically comprise porous plates or meshes facing the bed. The bed supports have pores with diameter significantly smaller than the average diameter of the particles in the bed. Liquid is conveyed via a coarse channel distributor through the bed support into the bed and on the outlet side the liquid passes through the other bed support via a distributor into the outlet. The bed supports can during use be contaminated both by small bed particles (fines) entering into the pores of the supports (plugging) and by fouling, i.e. deposition of particulate or precipitated material originating from the liquid passed through the column. Such contamination will lead to increased back pressures and may also cause inhomogeneities in the flow distribution of the column which will affect the performance negatively.
In e.g. the biopharmaceutical industry it is common practice to use the packed bed in a chromatography column for a large number of separation cycles. When the lifetime of the packed bed has been reached, the column is unpacked and repacked with a new bed. In older types of chromatography columns the unpacking and repacking necessitated disassembly of the column and it was then easy to inspect the bed supports and replace or clean them if needed. Modern chromatography columns can however be unpacked and repacked without disassembly through the use of packing/unpacking nozzles, as described in e.g. WO96/10451, WO99/22234, WO2008/134413 and U.S. Pat. No. 6,190,560. Disassembly of the column only in order to inspect and/or exchange the bed supports is cumbersome and costly and also involves a risk of accidental contamination of the flowpaths and there is therefore a need for a method to assess the cleanness of each bed support without disassembling the column.